Investigation of replication capability and filling mechanism of polymeric films micro structures with variable aspect ratios in thermal nanoimprinting process

• A star pattern with variable aspect ratios is used to evaluate the replication limit of T-NIL. • Polymer filling and demolding behavior in star pattern are investigated using FEA method. • When the aspect ratio is over 0.625, the polymer presents insufficient flow ability in mold. Thermal nanoimprinting lithography (T-NIL) is a high-resolution, low-cost nanofabrication technique that mechanically transfers mold pattern made by electroforming onto a thermoplastic polymeric film under high temperature and pressure conditions. Establishing a unified standard and characterization method for rapidly evaluating and accurately predicting the replication accuracy of high aspect ratio polymeric micro structures in T-NIL is of paramount significance. This study for the first time proposes a star-shaped pattern with line widths continuously varying from 40-320 μm, corresponding to variable aspect ratios of 0.3125–2.5. This pattern design allows for rapid evaluation of the replication accuracy of variable aspect ratio polymeric micro structures. Based on designed pattern, numerical simulations and experimental validation are conducted to reveal the effects of micro structural dimensions, material properties, and T-NIL process parameters on polymer filling behavior and replication accuracy. The results indicate that as aspect ratio is greater than 0.625, the micro structure has poor replication and low filling effect due to insufficient polymer viscoelastic deformation ability. When the line width exceeds 240 μm (aspect ratio of 0.417), the polymer is easily filled into mold achieving better replication accuracy and a filling rate of 99 % is achieved in 320 μm wide. In addition, the results also reveal that the high temperature and extending holding time significantly promote the viscoelastic deformation and filling abilities of polymer in high aspect ratio structure. This study offers significant insight into fast identifying the replication limits and accuracy of polymeric films using T-NIL process, which is crucial for high precision fabrication of polymeric microfluidic chips and micro optics.